Static Test Compaction for Scan Circuits by Using Restoration to Modify and Remove Tests

This paper describes a new approach to static test compaction for scan circuits that modifies tests in order to reduce the number of tests in a test set. The main contribution of this paper is a procedure referred to as restoration. In a basic step, the restoration procedure considers two tests, t_rem and t_mod, with sets of detected faults D_rem and D_mod, respectively. Starting from t_new = t_mod, and considering t_new as a variation of t_rem, the procedure restores bits of t_rem into t_new as necessary to ensure that faults from D_rem are detected by t_new. The procedure then restores bits of t_mod into t_new as necessary to ensure that all the faults from D_mod are detected by t_new. The test t_new is used for replacing t_mod, and the faults it detects out of D_rem are moved to D_mod. After several such steps, if Drem becomes empty, t_rem can be removed from the test set. The procedure is applied to test sets that are already compacted. The results show that the procedure can achieve significant additional compaction even without considering all the tests for removal or modification.